1. Field of Invention
This invention relates generally to chromophores having two-photon or multi-photon absorptivity.
2. Related Art
Organic molecules that absorb two or more photons simultaneously have wide application in a variety of technologies involving such subjects as thin film transistors, light emitting diodes, optical data storage, 3-D microfabrication techniques, host structures providing polar environments and precluding fluorescence quenching, and initiators of polymerization reactions. Two features of the two-photon absorption process make these applications feasible. The first is the quadratic dependence of two-photon absorption on the intensity of the incident radiation. This allows for three dimensional spatial resolution. The second feature is the absence of single-photon absorption, which allows an incident light beam to penetrate deeper into a material than would be possible with single-photon approaches.
Two photon or multi-photon absorbing molecules have been designed based on conjugated pi-electron systems with donating groups at each end of the pi-electron system providing charge-transfer properties. For example, U.S. Pat. Nos. 6,267,913 and 6,608,228, both incorporated by reference herein, describe two photon absorption chromophores having electron donors such as amino or alkoxy groups attached to a bridge of pi-conjugated bonds. The absorption of two or more photons by such molecules can trigger chemical and physical changes that make these molecules useful for two-photon applications. Although much progress has been made in developing two-photon or multi-photon molecules, additional two-photon or multi-photon absorbing materials, especially water-soluble materials, are needed to fully exploit two-photon applications.